Do female hummingbirds get fat before laying eggs?

Female hummingbirds do gain weight before laying eggs in order to have enough resources to produce eggs. The amount of weight gain depends on the species, but can be a substantial percentage of their normal body weight.

Why Do Female Hummingbirds Gain Weight?

Female hummingbirds gain weight prior to breeding for a few key reasons:

• To develop eggs – Producing eggs requires significant energy and resources. Female hummingbirds gain weight to store the fat and protein necessary to form egg yolks.
• To have energy for nesting – Nest building, incubating eggs, and caring for hatchlings are all energetically demanding activities. The extra weight gain provides the energy needed for these behaviors.
• To survive periods of starvation – Incubating eggs and caring for newborns means female hummingbirds cannot spend as much time foraging. The extra fat stores help sustain them when food is limited.

How Much Weight Do They Gain?

The magnitude of pre-breeding weight gain depends on the species:

• Ruby-throated hummingbird females may gain 25-40% more body weight.
• Rufous hummingbird females may nearly double their weight before breeding.
• Calliope hummingbird females may increase body weight by 30-50%.
• Broad-tailed hummingbird females may gain around 20% of extra body weight.

In most species studied, females gain between 20-50% more weight than their non-breeding weight in order to support reproduction.

When Does Weight Gain Occur?

The timing of pre-breeding weight gain corresponds with the breeding season:

• In northern regions, hummingbirds breed during spring and early summer.
• In southern regions closer to the equator, breeding may occur in fall and winter.
• Regardless of location, weight gain begins a few weeks prior to breeding.

By starting to gain weight well before eggs are laid, female hummingbirds ensure they have sufficient fat stores for the energy demands to come.

How Do They Gain So Much Weight?

Female hummingbirds put on weight rapidly leading up to breeding by:

• Consuming more food – Up to double normal intake.
• Optimizing foraging efficiency – Spending more time feeding.
• Storing extra calories as fat – Mostly around chest and abdomen.
• Altering hormone levels – Estrogen signals the body to store fat.

This coordinated physiological shift enables the necessary fat storage despite hummingbirds’ famously high metabolic rates.

Where Does the Fat Go Afterwards?

The extra fat provides energy for breeding and largely disappears over the course of:

• Egg production – Forming eggs consumes fat stores.
• Nesting period – Incubating eggs and rearing hatchlings requires energy.
• Post-breeding recovery – Replenishing exhausted resources after offspring fledge.

By the end of breeding activities, female hummingbirds have used up most of the extra fat and return close to their normal non-breeding weight.

Do Males Gain Weight Too?

Male hummingbirds generally do not gain as much pre-breeding weight as females, but they do undergo some physiological changes:

• Moderate weight gain – Up to 10%, mostly around chest.
• Enlarged liver and pancreas – To power energetically demanding courtship displays.
• Increased fat storage – Provides energy for courtship and finding food for the female.

While male weight gain is modest compared to females, they too require extra energy reserves for breeding activities like courtship feeding.

Does Weight Gain Impact Hummingbird Behavior?

The extra weight female hummingbirds carry during breeding season does impact some aspects of their behavior:

• Reduced maneuverability – Heavier bodies are less agile in flight.
• Changes to feeding style – Shorter hovering times, more perched feeding.
• Decreased territoriality – Less energetic defense of feeding patches when laden with fat.
• Higher food intake – Actively seeks out more flower patches and feeders.

However, these breeding-related changes are temporary until females revert back to their normal weight post-breeding.

Why Don’t Hummingbirds Get Too Heavy to Fly?

Despite doubling their body weight in some species, female hummingbirds remain able to fly due to:\r\n

• Extremely high wingbeat frequency – Up to 80 beats per second provides the necessary lift.
• Adaptations for aerial agility – Lightweight bills, reduced number of tail feathers, etc.
• Selective fat storage – Accumulating mostly around the abdomen keeps the wings light.
• Seasonal adjustments – Altering behavior to compensate for reduced maneuverability.

So while heavy, the strategic fat stores do not prevent females from supporting their weight in flight during breeding.

Does Weight Gain Lead to More Eggs?

The pre-breeding weight gain positively influences reproductive output:

• Enables more egg production – Each egg may represent 10-20% of female’s body weight.
• Provides nutrients for egg development – Especially protein for egg yolk formation.
• Boosts likelihood of renesting – If a clutch fails, extra reserves allow another attempt.

Heavier females at the onset of breeding are able to lay larger clutches over more attempts, increasing chances of successfully fledging young.

How Many Eggs Do Hummingbirds Lay?

The number of eggs in a clutch ranges by species, but commonly:

• Ruby-throated hummingbirds – 2-3 eggs per clutch.
• Black-chinned hummingbirds – 2 eggs per clutch on average.
• Anna’s hummingbirds – 2-3 per clutch, occasionally up to 6.
• Rufous hummingbirds – Often just 2 eggs laid per breeding attempt.

Larger species like magnificent and blue-throated hummingbirds may lay more eggs, while smaller species lay fewer. But most lay 1-3 eggs, replenishing from fat stores between breeding attempts.

Data on Pre-breeding Weight Gain by Species

Key Takeaways

In summary, female hummingbirds undergo dramatic pre-breeding weight gain across species, enabled by:

• Doubling food intake leading up to breeding season
• Storing excess calories as fat, primarily around the abdomen
• Alterations in hormones that shift metabolism towards fat storage

This extra weight, often representing a 20-50% increase over normal levels, provides the crucial energy reserves needed to successfully lay eggs and rear offspring. The fat is gradually depleted over the course of nesting activities until the females return to their typical non-breeding weight.

Conclusion

Pre-breeding weight gain is an essential adaptation that improves reproductive success in female hummingbirds across species. By strategically accumulating substantial fat stores, females equip themselves with the nutrients and energy necessary to sustain the demands of egg production, nesting, and raising chicks. Their optimized physiological shift enables breeding behaviors that would otherwise not be possible for a tiny bird with an extremely high metabolism. So while the extra weight may slow them down a bit, it allows female hummingbirds to carry out the incredible physiological feat of reproduction.